Systems and methods for recognizing human's activities in a space such as an office or a factory where many people are active while sitting or moving are known. If the system can detect whether or not there is a person in a space, the system can be used to judge whether people remain present in the space so as to improve security. Such a system can also be used for monitoring and reducing corporate internal crime and for the management of employee working hours.
For example, Japanese Unexamined Patent Publication No. 2015-132443 describes a sensor that detects heat emitted by a person as a means to detect a person in a certain space. For example, a thermopile sensor can measure the surface temperature of a remote object. By arranging a plurality of thermopile sensors in an array, the plurality of thermopile sensors can measure the temperature of the space for each of the cells partitioned into 4×4, 8×8 or even finer meshes. That is, by using a thermopile sensor, it becomes possible to detect the presence or absence of a person in a space.